Approximately 100 antibiotics are in use today, 15 in phase 2 or 3 clinical studies, 13 of which are against multi drug-resistant gram-positive and 2 against extended spectrum β-lactamase producing gram-negative bacteria. Heavy antibiotic use and communal spread of bacteria have greatly increased antibiotic resistance, and this problem is continually increasing in severity. The bacterium Pseudomonas aeruginosa (Pa) is a prime example: 30% of clinical isolates from intensive care unit (ICU) or nursing home patients are now resistant to 3 or more drugs, and a similar situation exists for other organisms. Another reason why conventional antibiotics generally work poorly in chronic infections is that the infecting organisms live in biofilms, which are surface-associated bacterial communities encased in a complex biopolymeric matrix. Physiological changes inherent to biofilm growth make bacteria far more resistant to killing by the immune system and antibiotics than cells in the free-living (planktonic) state. Examples of biofilm infections include the airway infections in cystic fibrosis (CF) patients, chronic wound and sinus infections, endocarditis, and medical device infections, among others.
The prominence of Pa infection and its impact on the lungs of CF patients is well documented (Fick (1989) Chest 96:158-164; Hoiby (1993) Annu Rev. Med. 44:1-10). Existing therapies, such as aminoglycoside antibiotics, eventually have little or no impact on disease progression and ultimately, 80-95% of CF patients succumb to respiratory failure due to chronic Pa infection and airway inflammation. Despite recent advances in disease management, the lungs of CF patients are particularly susceptible to chronic bacterial infections. Moreover, current therapies to control Pa infections in CF patients are inconvenient and with modest impact on mortality. There is a consensus that because Pa resides in the lung at the tissue-air interface, the most effective route of antibiotics drug delivery is locally by direct inhalation. The current standard of care to treat Pa infection in CF patients is twice-daily treatment of tobramycin solution administered by oral inhalation for alternating 28-day on-off cycles. The drug administration involves nebulizer priming, followed by approximately half an hour of inhalation at each dosing. Given that CF patients are increasingly burdened with multiple treatment regimens on an average day, the quality of life has become an important factor in the development of new drug therapies; for example, nearly three hours of the day are spent dealing with inhalation therapy (i.e. saline solution, antibiotic and DNase treatment) (Geller, D. E., et al (2007) Pediatric Pulmonology 42:307-313).
Inhaled tobramycin solution represents a significant advancement in treating pulmonary infection in CF patients. Further improvements have been enabled by recent advances in powder engineering, allowing for additional reduction in dose level as well as dosing time. For example, inhalation of tobramycin dry powder produced serum tobramycin PK profiles comparable to those obtained via nebulization, with a significant reduction in dose and shorter administration time. Four capsules of 28 mg (total tobramycin dose 112 mg) produced comparable systemic exposure to 300 mg inhaled nebulized solution, in less than one-third the administration time (Geller, D. E., et al (2007) Pediatric Pulmonology 42:307-313). In addition, tobramycin dry powder increased the local lung exposure, increasing efficacy, and reduced systemic exposure, thereby reducing systemic side effects. The data demonstrated that recent technological improvements in particle engineering and in inhalation devices have enabled a fast, safe, and efficacious delivery of high payload of powder even to the already susceptible CF patients' lungs. However, despite the delivery advances which achieved higher local tobramycin concentrations and delayed the onset of bacterial resistance development, the occurrence of Pa-resistant strains continues (Plasencia, V., et al (2007) Antimicrobial Agents Chemotherapy 51:2574-2581). Therefore, there is not only a need for new classes of safe and efficacious anti-infective agents, but ones that can be delivered locally to the lung with simple and convenient administration experience.
The effectiveness of gallium against Pa has stimulated interests in developing this drug candidate for CF lung infections. For many years, gallium has been used for the treatment of several human and animal disorders, including hypocalcaemia and osteoporosis (Warell et al., U.S. Pat. No. 4,529,593; Bockman et al., U.S. Pat. No. 4,704,277; Bradley et al., U.S. Pat. No. 5,196,412; Bradley et al., U.S. Pat. No. 5,281,578), cancer (Adamson et al. (1975) Cancer Chemothe. Rept 59:599-610; Foster et al. (1986) Cancer Treat Rep 70:1311-1319; Chitambar et al. (1997) Am. J. Clin. Oncol. 20:173-178), wound healing and tissue repair (Bockman et al., U.S. Pat. No. 5,556,645; Bockman et al., U.S. Pat. No. 6,287,606), as well as both intracellular and extracellular infections (Schlesinger et al., U.S. Pat. No. 5,997,912; Schlesinger et al., U.S. Pat. No. 6,203,822; Bernstein, et al., International Patent Application Publication no. WO 03/053347; Perl, U.S. 2008/0241275). These patent documents, and any U.S. counterparts, are expressly incorporated herein by reference. Gallium was shown to be both bacterial growth inhibiting as well as bactericidal as the minimum inhibitory concentration (MIC90) and bactericidal concentration (MBC) of gallium against Pa are both approximately 0.7 μg/mL (Kaneko et al. (2007) J. Clin. Invest. 117:877-888). Gallium nitrate has demonstrated strong bactericidal activity against many gram-negative and gram-positive bacteria. The effectiveness of gallium nitrate against a variety of bacteria found to chronically colonize the lungs of CF patients, such as Pseudomonas aeruginosa, Burkholderia cepacia, and methycillin-resistant Staphylococcus aureus (MRSA), makes it a promising drug candidate for treatment in CF.
Local delivery is often the most effective method to maximize bioavailability to the target site while minimizing systemic exposure. For local lung delivery to treat lung infections, there is evidence demonstrating that localized delivery of gallium nitrate to the respiratory tract is protective in mouse Pa challenge models (Kaneko et al. (2007) J. Clin. Invest. 117:877-888). In these studies, intratracheal (i.t.) inoculation of a lethal dose of Pa followed by nasal instillation of a bolus of liquid containing gallium nitrate resulted in good protection, even under in vivo Pa biofilm colonization conditions. While nasal instillation of a bolus dose is frequently used in many mouse lung studies, it is known that delivering liquid aerosols through the nasal route resulted in poor (less than 10% of delivered dose) lung penetration, most likely due to inertial impaction of the aerosol droplets onto the tortuous anatomical structures in the nasal cavity (Bryant et al. (1999) Nucl. Med. Commun. 20:171-174). Thus the minimal gallium-protective dose observed for the nasal administration route is likely significantly higher than direct i.t. application or if pulmonary inhalation is used.
The current invention is a high concentration liquid formulation for gallium containing compounds that could be efficiently delivered from conventional nebulizers with short (<10 minutes) dosing times. Optimum formulation for such liquid gallium composition may require a minimum amount of counterion, such as citrate, to buffer against lung fluid to prevent gallium precipitation. Furthermore, the aerosol droplet size may be modulated by incorporating viscosity-enhancing components, such as mannitol, which in addition may be used to adjust the osmolality of the gallium composition. The increased viscosity of the gallium composition may also impact the time required to deliver the necessary dose. Similar effects on droplet size and delivery time may be observed by increasing the ionic strength of the gallium composition. A successful powder formulation for inhalation requires optimal balance among several physicochemical attributes including geometric and aerodynamic particle size, physical and chemical stability as well as aerosol dispersibility. A second key inventive contribution is a room temperature stable inhalable dry powder formulation of gallium with the appropriate aerosol properties for deep lung delivery using commercially available dry powder inhalers (such as Tubohaler™, Cyclohaler™, Turbospinhaler™). The formulations resulted in gallium nitrate dosage forms that are compatible with simple, cost-effective, portable dry powder inhalers that can be conveniently and easily self-administered. Spray drying was used to prepare the gallium nitrate dry powder for inhalation. For inhalable dry powder manufacturing, spray drying is the method of choice as it is the most effective and direct process to manufacture powders with appropriate aerosol properties for deep lung delivery. Its use has been demonstrated with tobramycin dry powder (Duddu, S. P., et al. (2002) Pharmaceutical Research 19:689-695), and with inhaled insulin product Exubera™, the first protein to be delivered through the pulmonary route (White, S., et al. (2005) Diabetes Technology & Therapeutics 7, 896-906). Spray drying is an ideal process to create homogeneous particles containing precise amounts of drug and excipients which can be engineered to perform in a predictable manner with a handheld delivery device. The feasibility of preparing spray dried powders containing antibiotics has been previously demonstrated (Lechuga-Ballesteros, et al. (2008) J. Pharm. Sci. 97:287-302).